U.S. Pat. No. 3,931,354 teaches that a chemically stable advanced composite could be made from a functionally terminated polybutadiene polymer that has been reacted with an epoxide and crosslinked with a bismaleimide crosslinking agent and a peroxide free radical initiator. The major advantages possessed by the compositions described in U.S. Pat. No. 3,931,354 are vacuum bag processing and resistance to moisture. Although the reference system solved the problem of resistance to high humidity environments, full scale development of the system has been retarded due to the undesirable characteristics of low transverse tensile strain-to-failure property. This property is one measurement of the resin toughness. Greater toughness is required in modern structural designs made from resins. Such structures are ailerons, aircraft tail assemblies, and radomes, for example. In these structures the resins are used as high performance binders for graphite, carbon fibers, boron filaments, and glassfiber reinforcements.